The present invention relates to a method or a system for fabrication of semiconductor integrated circuits; more particularly, the present invention relates to a method and a system for controlling dummy dispense of a liquid within fabrication of semiconductor integrated circuits.
Photolithography is an essential part in semiconductor fabrication. Usually, it includes the following steps: coating of a photoresist layer, exposure to a light source, and developing by developer. When the photoresist layer is irradiated by a light source, the irradiated photoresist will transform to, or generate acid. After contacting with a developer, usually an alkali solution, the irradiated photoresist reacts with the developer, but the non-irradiated portion does not. Therefore, a positive or negative image of a mask is transformed on the substrate.
When sub-micron or deep sub-micron technologies are generally used within semiconductor integrated circuits, the photoresist coating process is more important and difficult to control. Usually, a tracker for a photoresist coating has two or more different photoresists responding to different photoresist coating recipes. The different photoresists in the tracker are conveyed separately to different nozzles by conduits to avoid contamination. Because of the mass production of semiconductor integrated circuits, one of the photoresists in a tracker usually runs out sooner than the others. Under this situation, some photoresists may not be used for a particular period of time. Because the photoresist is a volatile solution, the solvent of the photoresist tends to evaporate when the photoresist is exposed to air. As a result, the nozzle becomes clogged by photoresist due to the evaporation of the solvent when the photoresist is not used. If the clogged nozzle dispenses photoresist on a silicon wafer, poor wafer coating frequently occurs and leads to rework of the photolithographic process, or low yield of the product. In order to avoid nozzle clogging, the conventional method has two approaches. First, a dummy dispense is performed. The time to perform each dummy dispense is set to reoccur as time passes. For example, a dummy dispense depends on different settings to reoccur corresponding to different liquids. Second, a dummy dispense is performed prior to coating a photoresist layer on the first wafer of each lot.
FIG. 1 shows a result generated from a traditional technique used to control dummy dispense within fabrication of semiconductor integrated circuits. Usually, it takes 30 minutes for coating a photoresist layer on a manufacturing lot of wafers, for example, 24 pieces during a photoresist coating process. In a continuous photoresist coating process, four lots of wafers can be processed in 2 hours. Based on traditional approaches, six dummy dispenses are required in two hours. However, most of the dummy dispenses are not necessary when the photoresist coating process for different lots is continuous. For example, the second to the sixth dummy dispenses are not required when the nozzle does not become clogged in the continuous photoresist coating process. Accordingly, the conventional dummy-dispense process will increase the cost of fabricating semiconductor integrated circuits due to the unnecessary dummy dispenses.
Accordingly, it is desirable to provide a method and a control system to reduce the manufacturing cost and improve productivity as well.